When printing with a color inkjet printer, all colors are applied to the paper at once. Each color generally ends up where it is expected. When printing with a commercial printing press, a document consisting of more than one color of ink requires that the single page pass through the printing press multiple times as each color is applied to the paper. Sometimes the paper or the plates applying the ink may shift. It may be a tiny shift but sufficient to be noticeable. For example, a white gap may appear between a letter of a first color (e.g., yellow) that is supposed to be touching a box of a second color (e.g., blue). When this happens, the color is said to be out-of-register. Color-to-color misregistration refers to misregistration between color separations in a printed image. Such misregistration in printed halftoned images may result in image defects, a primary one being white gaps between color edges.
A trapping filter may be used to address the misregistration in the image by introducing a perceptually dominant third color. The trapping filter may include a “trap” around the object that is the third color, which may be a mixture of the first two colors (e.g., green). Conventional traps have a uniform thickness. A uniform thickness may work well for orthogonal objects and objects with few irregularities. However, conventional trap filters do not account for the size (e.g., extension) of the object in non-orthogonal directions or irregularities in the object. What is needed is an improved trap filter that accounts for the size of the object in non-orthogonal directions and irregularities in the object.